Auto merge of #122362 - Zoxc:rustc_driver_static_std, r=oli-obk,lqd,bjorn3,Kobzol

Link `std` statically in `rustc_driver`

This makes `rustc_driver` statically link to `std`. This is done by not passing `-C prefer-dynamic` when building `rustc_driver`. However building `rustc-main` won't work currently as it tries to dynamically link to both `rustc_driver` and `std` resulting in a crate graph with `std` duplicated. To fix that new command line option `-Z prefer_deps_of_dynamic` is added which prevents linking to a dylib if there's a static variant of it already statically linked into another dylib dependency.

The main motivation for this change is to enable `#[global_allocator]` to be used in `rustc_driver` allowing overriding the allocator used in rustc on all platforms.

---

Instead of adding `-Z prefer_deps_of_dynamic`, this PR is changed to crate opt-in to the linking change via the `rustc_private` feature instead, as that would be typically needed to link to `rustc_driver` anyway.

---

try-job: aarch64-apple
try-job: x86_64-msvc
try-job: i686-mingw
try-job: dist-x86_64-msvc
try-job: aarch64-gnu

2 files changed, 34 insertions, 4 deletions

diff --git a/src/bootstrap/src/bin/rustc.rs b/src/bootstrap/src/bin/rustc.rs
index 011c289d932..d04e2fbeb78 100644
--- a/src/bootstrap/src/bin/rustc.rs
+++ b/src/bootstrap/src/bin/rustc.rs
@@ -89,6 +89,25 @@ fn main() {
         rustc_real
     };
 
+    // Get the name of the crate we're compiling, if any.
+    let crate_name = parse_value_from_args(&orig_args, "--crate-name");
+
+    // When statically linking `std` into `rustc_driver`, remove `-C prefer-dynamic`
+    if env::var("RUSTC_LINK_STD_INTO_RUSTC_DRIVER").unwrap() == "1"
+        && crate_name == Some("rustc_driver")
+        && stage != "0"
+    {
+        if let Some(pos) = args.iter().enumerate().position(|(i, a)| {
+            a == "-C" && args.get(i + 1).map(|a| a == "prefer-dynamic").unwrap_or(false)
+        }) {
+            args.remove(pos);
+            args.remove(pos);
+        }
+        if let Some(pos) = args.iter().position(|a| a == "-Cprefer-dynamic") {
+            args.remove(pos);
+        }
+    }
+
     let mut cmd = match env::var_os("RUSTC_WRAPPER_REAL") {
         Some(wrapper) if !wrapper.is_empty() => {
             let mut cmd = Command::new(wrapper);
@@ -99,9 +118,6 @@ fn main() {
     };
     cmd.args(&args).env(dylib_path_var(), env::join_paths(&dylib_path).unwrap());
 
-    // Get the name of the crate we're compiling, if any.
-    let crate_name = parse_value_from_args(&orig_args, "--crate-name");
-
     if let Some(crate_name) = crate_name {
         if let Some(target) = env::var_os("RUSTC_TIME") {
             if target == "all"
diff --git a/src/bootstrap/src/core/builder.rs b/src/bootstrap/src/core/builder.rs
index 84c23c059e9..ccdeb442af4 100644
--- a/src/bootstrap/src/core/builder.rs
+++ b/src/bootstrap/src/core/builder.rs
@@ -1106,6 +1106,12 @@ impl<'a> Builder<'a> {
         StepDescription::run(v, self, paths);
     }
 
+    /// Returns if `std` should be statically linked into `rustc_driver`.
+    /// It's currently not done on `windows-gnu` due to linker bugs.
+    pub fn link_std_into_rustc_driver(&self, target: TargetSelection) -> bool {
+        !target.triple.ends_with("-windows-gnu")
+    }
+
     /// Obtain a compiler at a given stage and for a given host (i.e., this is the target that the
     /// compiler will run on, *not* the target it will build code for). Explicitly does not take
     /// `Compiler` since all `Compiler` instances are meant to be obtained through this function,
@@ -2162,10 +2168,18 @@ impl<'a> Builder<'a> {
         // When we build Rust dylibs they're all intended for intermediate
         // usage, so make sure we pass the -Cprefer-dynamic flag instead of
         // linking all deps statically into the dylib.
-        if matches!(mode, Mode::Std | Mode::Rustc) {
+        if matches!(mode, Mode::Std) {
+            rustflags.arg("-Cprefer-dynamic");
+        }
+        if matches!(mode, Mode::Rustc) && !self.link_std_into_rustc_driver(target) {
             rustflags.arg("-Cprefer-dynamic");
         }
 
+        cargo.env(
+            "RUSTC_LINK_STD_INTO_RUSTC_DRIVER",
+            if self.link_std_into_rustc_driver(target) { "1" } else { "0" },
+        );
+
         // When building incrementally we default to a lower ThinLTO import limit
         // (unless explicitly specified otherwise). This will produce a somewhat
         // slower code but give way better compile times.